NAME

SYNOPSIS

DESCRIPTION

The setenv() function shall update or add a variable in the environment of the calling process. The envname
argument points to a string containing the name of an environment variable to be added or altered. The environment variable shall
be set to the value to which envval points. The function shall fail if envname points to a string which contains an
'=' character. If the environment variable named by envname already exists and the value of overwrite is
non-zero, the function shall return success and the environment shall be updated. If the environment variable named by
envname already exists and the value of overwrite is zero, the function shall return success and the environment
shall remain unchanged.

If the application modifies environ or the pointers to which it points, the behavior of setenv() is undefined. The
setenv() function shall update the list of pointers to which environ points.

The strings described by envname and envval are copied by this function.

The setenv() function need not be reentrant. A function that is not required to be reentrant is not required to be
thread-safe.

RETURN VALUE

Upon successful completion, zero shall be returned. Otherwise, -1 shall be returned, errno set to indicate the error, and
the environment shall be unchanged.

ERRORS

The setenv() function shall fail if:

[EINVAL]

The name argument is a null pointer, points to an empty string, or points to a string containing an '='
character.

[ENOMEM]

Insufficient memory was available to add a variable or its value to the environment.

The following sections are informative.

EXAMPLES

None.

APPLICATION USAGE

See exec() , for restrictions on changing the environment in
multi-threaded applications.

RATIONALE

Unanticipated results may occur if setenv() changes the external variable environ. In particular, if the optional
envp argument to main() is present, it is not changed, and thus may point to an obsolete copy of the environment (as
may any other copy of environ). However, other than the aforementioned restriction, the developers of
IEEE Std 1003.1-2001 intended that the traditional method of walking through the environment by way of the environ
pointer must be supported.

It was decided that setenv() should be required by this revision because it addresses a piece of missing functionality,
and does not impose a significant burden on the implementor.

There was considerable debate as to whether the System V putenv() function or the
BSD setenv() function should be required as a mandatory function. The setenv() function was chosen because it
permitted the implementation of the unsetenv() function to delete environmental
variables, without specifying an additional interface. The putenv() function is
available as an XSI extension.

The standard developers considered requiring that setenv() indicate an error when a call to it would result in exceeding
{ARG_MAX}. The requirement was rejected since the condition might be temporary, with the application eventually reducing the
environment size. The ultimate success or failure depends on the size at the time of a call to exec, which returns an indication of this error condition.